Measurement of forces and moments using strain-gaged load transducers is well known in the art. A typical transducer utilizes an elastic element which deforms under the applied load. Single or multiple strain gages attached to this elastic element convert the mechanical deformations of the said element into electrical signal(s), which can be measured by appropriate instrumentation. Thus, the applied load can be determined from the measured signals.
Traditionally, a load cell has been instrumented with as many independent strain-gaged channels as the number of desired outputs, or the number of degrees of freedom desired to be measured at the output. When several load cells are used as part of a single system to measure the six independent loads, or degrees of freedom possible, the appropriate gages in the load cells are interconnected to provide the output signals. An example of such a transducer is known as a force plate or a force platform.
All force plates make use of the specialized geometry of the load cells themselves, or the position and orientation of the strain gages, or both, to measure the desired loads. Current force plates utilize two, three, or four load cells, the latter being the most commonly used design. In these current designs, the three force components at each load cell are individually measured and summed up. However, the moment components are not individually measured at each load cell. For example, in a design utilizing four load cells, two of the moment components are obtained from the differences between the vertical force components in the load cells, and the torque is determined by summing shear forces about the center of the force plate. Designs utilizing two and three load cells have similar measurement methods. These types of designs introduce limitations and possible errors. For example: first, building force plates with large spans between the load cells results in relatively low natural frequencies or undesirably large instrument heights; second, mounting the load cells either to a rigid base plate or a rigid external surface is a general requirement.
The present invention relates to both single and multi-component load transducers utilizing multiple load cells as an integral part of the design. In each load cell, at least as many independent channels as the load components transmitted by the load cell are measured. Therefore, all the load components are accounted for utilizing independent force and moment measurements from the individual load cells. The present invention also includes designs where channels from different individual load cells are interconnected. Thus, the errors and limitations from the prior art (as noted above) are greatly reduced.
The invention described herein relates to the measurement of forces and moments utilizing multiple load cells (otherwise known and referred to as xe2x80x9cpylonsxe2x80x9d) which form an integral part of a system (a xe2x80x9ctransducerxe2x80x9d, otherwise known and referred to as a xe2x80x9cforce platexe2x80x9d or a xe2x80x9cforce platformxe2x80x9d) or a combination of multiple systems (a force plate or force platform xe2x80x9carrayxe2x80x9d). Each pylon is capable of measuring all six degrees of forces and moments (the vertical force, the two orthogonal shear forces, and the three moments, one about each orthogonal axis) via strain gages attached to the pylons. In this invention, the pylons are attached to a top plate, and can be fitted with an optional bottom plate and an optional mounting plate. The signal produced by the gages can be transmitted via wiring or wireless means directly to a data collection device, and, alternatively through a connector board, then to a pre-amplifier, then an amplifier, then finally to a data collection device. The output may be six or more channels, and can be electronically combined to six channels.
By measuring with two or more pylons, whereby each pylon measures all components of force and moment, measurement errors will be greatly reduced, including cross-sensitivity and, thereby, cross-talk. Thus, with independent measurements, assumption and calculation errors are greatly reduced.